A communication system to be mounted on a car is conventionally adopted in which electronic control units (ECUs) controlling operations of appliances mounted on the car are connected to each other by connecting buses for multiplex communication to each other via a relay connection unit (gateway) to construct a network so that the relay connection unit relays messages sent and received among the ECUs belonging to different buses.
In recent years, owing to high functionality and performance of the car, the number of appliances to be mounted on the car has increased, and the number of messages to be relayed by the relay connection unit has also rapidly increased. When a large number of messages are sent to the relay connection unit, all the messages cannot be instantly relayed, and messages to be relayed stay inside the relay connection unit, which leads to delay in relaying the messages. Therefore the relay connection unit is desired to execute relay processing at a high speed.
Thus as disclosed in Japanese Patent Application Laid-Open No. 2006-352235 (patent document 1), there is proposed the construction in which the relay processing of the relay connection unit is executed not by software of a CPU but by hardware. As relay processing, the relay connection unit conventionally executes destination search processing of specifying a destination to which a message is to be sent and switching processing of switching a fixed length cell of the message. But in the patent document 1, the destination search processing and the switching processing are executed not by the CPU but by the search engine and the self-routing module both constructed of hardware.
Therefore the processing performance of the CPU does not adversely affect the relay speed of a message, and thereby it is possible to decrease delay in the relay of the message which is caused by low processing performance of the CPU.
In the above-described communication system to be mounted on the car, there is a case where each ECU and the relay connection unit have a network management function. The network management function means a function of initializing the ECUs connected with the buses, actuating the network, setting the network, detecting and processing the operational states of the ECUs and the network, sending signals, reading and setting parameters of the ECUs and the like in sending and receiving ring messages between the ECUs and the relay connection unit. Owing to the network management function, safety and reliability are ensured in the communication between the ECUs and the relay connection unit.
In the processing to be executed by the network management functions, specifications of parameters such as timer values, error counter thresholds, and the like are used.
But when the network management function is constructed of the hardware as disclosed in the patent document 1, the specifications of the parameters and the like to be used in each processing are incorporated in the hardware. Thus in altering the specification, it is necessary to alter the construction of the hardware. Therefore the construction disclosed in the patent document 1 has a problem that it is difficult to alter the specifications.
Because these specifications are different according to models of cars, it is necessary to construct the network management function of the hardware for each model. Thus the construction disclosed in the patent document 1 has a problem that it is impossible to commonly use the network management function constructed of the hardware.
Patent document: Japanese Patent Application Laid-Open No. 2006-352235